In recent years, there has been a drastic advance in the technique of manufacturing a thin film transistor (hereinafter referred to as “TFT”) on a substrate. In particular, efforts of development have been made to apply this technology to the drive element for an active matrix large-screen display apparatus. The Si-based inorganic materials such as a-Si or poly-Si are used as semiconductor materials to manufacture TFTs which are currently in commercial use. The production of TFTs using such inorganic materials requires use of a vacuum process and high-temperature process, which processes have a great impact on the production cost.
To solve these problems, studies have been made to produce TFTs using organic materials (hereinafter also referred to as “organic TFT”) in recent years. Compared to inorganic materials, organic materials are characterized by a wide variety of options. In the production of organic TFTs, processes of excellent productivity such as a printing or coating process are used, instead of the above-mentioned vacuum process or high-temperature process. Therefore, the production cost is reduced. Further, organic TFTs can be formed on a flexible and less heat-resistant substrate exemplified by a plastic film, and is expected to be used to a wide range of field including a display with curved surface.
The conventional method for applying organic semiconductor materials includes liquid droplet applying techniques such as an inkjet method and a dispenser method, wherein the solution (hereinafter also referred to as “ink”) containing organic semiconductor materials dissolved or dispersed therein is applied directly on the substrate. These techniques: (1) does not require a vacuum process; (2) does not waste the material; and (3) permits direct patterning. Thus, these techniques have an advantage of eliminating the need for an etching process, compared to the photolithography method.
To ensure excellent electric property and high degree of reliability in the aforementioned organic TFT, it is necessary to form an organic semiconductor film having an appropriate film thickness with high accuracy at a prescribed position. However, when the aforementioned inkjet method or dispenser method is used to form an organic semiconductor film, before the applied ink gets dried and solidifies, it may spread, depending on the surface condition of the substrate (liquid-repellent or lyophilic properties) or drying atmosphere, to surrounding unwanted portions. When this happens, patterning failure will occur and sufficient film thickness cannot be obtained, with the result that excellent properties of organic TFT cannot be provided. To solve this problem, measures should be taken to prevent the applied ink from spreading out of prescribed regions.
In recent years, techniques using a droplet application technique have been studied, using an inorganic material or precursor as semiconductor materials. However, similarly to the case of the organic material, it is not easy to form a semiconductor film with appropriate thickness at a prescribed position with high accuracy either in this case.
Patent Document 1 discloses a thin film forming technique suitable for methods for producing organic EL elements using an organic semiconductor film, wherein a bank is provided on the edge of the region to which liquid material is applied to prevent the inkjet liquid droplet from flowing out of the applied region.